In an attempt to increase the efficiencies and performance of contemporary gas turbine engines, engineers have progressively pushed the engine environment to more extreme operating conditions. The harsh operating conditions of high temperature and pressure that are now frequently specified place increased demands on engine components and materials. Indeed the gradual improvement in engine design has come about in part due to the increased strength and durability of new materials that can withstand the operating conditions present in the modern gas turbine engines. With these changes in engine materials, there has arisen a corresponding need to develop new repair methods appropriate for such materials.
Components used in modern gas turbine engines are frequently castings from a class of materials known as superalloys. The superalloys include nickel-based, cobalt-based and iron-based superalloys. In the cast form, components made from advanced superalloys include many desirable properties such as high elevated-temperature strength and good environment resistance. Advantageously, the strength displayed by this material remains present even under stressful conditions, such as high temperature and high pressure, experienced during engine operation.
Disadvantageously, the superalloys generally are very difficult to weld successfully. Traditional repair methods have proven less than satisfactory for superalloy materials. During a high temperature welding for example, a superalloy component may experience severe heat stress and cracking, giving the component undesired properties for further engine service. Hence, it is desirable to find a repair method suitable for use with superalloys that does not subject the workpiece matrix to heat-induced damage.
Heating a component in pre-welding and post-welding steps with known devices such as induction heaters, quartz lamps, and heating blankets is also disadvantageous. These items are time consuming and difficult to deploy on a workpiece. Certain workpiece geometries are not suited to the use of such heating methods. Further, it is difficult to control and direct the heat generated by these devices.
The option of throwing out worn turbine engine components and replacing them with new ones is not an attractive alternative. Superalloy components can be expensive due to costly materials and manufacturing processes. For example, a high pressure turbine blade made of a superalloy can be quite costly to replace, and a single stage in a gas turbine engine may contain several dozen such blades. Moreover, a typical gas turbine engine can have multiple rows or stages of turbine blades. Consequently there is a strong financial need to find an acceptable repair method for superalloy turbine blades and vanes.
Hence, there is an ongoing need to identify improved repair methods for gas turbine engine superalloy components that address one or more of the above-noted drawbacks. Namely, a repair method is needed that can weld superalloy components while avoiding heat induced cracking. Further a repair method is needed that can efficiently and effectively heat a workpiece in pre-welding and post-welding operations. Further, a repair method is needed that by virtue of the foregoing is therefore less costly as compared to the alternative of replacing worn parts with new ones. The present invention addresses one or more of these needs.